Method of eliminating offset in printing



United States Patent 3,236,179 METHOD OF ELKMINATING OFFSET IN PRINTING George F. Rooney, 31a, Winton Engineering Company, 2353 May St., Cincinnati 6, Ohio No Drawing. Filed June 19, 1961, Ser. No. 117,778 2 Claims. (Cl. 101416) This invention relates to a method of eliminating undesired offset printing and to a composition for use in eliminating such offset printing.

In various printing processes, newly printed sheets and the like are stacked one on top of another, and there may be undesired offset printing on sheets adjacent to and facing newly printed sheets. In the past, it has often been the practice to apply powdered starch of the like in the form of a dust to the faces of freshly printed sheets to prevent or minimize such undesired offset printing. Such starch powders adhere to the ink and can cause a rough finish on the ink if the starch particles are not very fine or small. If the starch powder is made sufficiently fine to avoid the formation of such a rough surface, it may not be fully effective in preventing offset printing.

I have found that a greatly improved offset prevention is obtained without providing a rough surface by use of a powder formed from hydrogenated castor oil or the like. This material can be ground to a fine powder of approximately 100 mesh size particles or smaller without loss of the power to prevent offset. A small amount of a finely divided phosphate such as tri-calciurn phosphate or aluminum phosphate and a small proportion of china clay can be added to render the powder free flowing. The particles of tri-calcium phosphate and of the china clay should be at least as fine as the powder particles and preferably are substantially finer.

Inspection of the powder when sprayed on a printed sheet indicates that the ink and powder grains do not adhere together as is the situation when starch powder is used to prevent offset. The powder can be sprayed on freshly printed sheets by use of commercial powder spraying devices of the type formerly used for spraying starch powders. A suitable device for spraying my improved powder is shown in my Patent No. 2,850,214.

The following example is given to illustrate the invention in greater detail, but it is to be understood that the example is given primarily by way of example rather than by way of limitation, except as set forth in the claims. In the following example all parts and percentages are taken by weight.

Example 200 parts of flakes of a commercial hydrogenated castor oil having an iodine value of from 2.0 to 4.0 and a titre of 70 to 75 degrees centigrade were pulverized in a hammermill until all would pass 100 mesh commercial screen. During pulverization, the partially pulverized hydrogenated castor oil was periodically removed from the mill and sieved, portions not passing the sieve being returned for further pulverizing. To the pulverized hydrogenated castor oil were added two parts of pulverized tri-calcium phosphate and one part of pulverized china clay. The phosphate, china clay, and pulverized hydrogenated castor oil were thoroughly mixed. The mixture was sprayed on the printed sheets in commercial offset eliminating spray equipment and was highly effective in eliminating offset.

The new powder is effective in preventing offset both with gloss inks and with flat inks. Since it does not stick to and is not wet by the ink, larger or coarser grain sizes can be used than with starch powders without fear of a resulting roughness of the sheet. Slight abrasive action such as the sliding of one sheet on top of another, loose-ns the material and permits it to fall off, for the most part, in subsequent handling.

The new powder is particularly valuable in preventing offset of printing on waxed cartons such as those used for frozen foods and the like. It can be sprayed on printed faces of such cartons. Thereafter, when the cartons are wax coated, the powder melts off because it has a lower melting point than the wax.

The powder composition and method of preventing offset printing described above are subject to variation without departing from the spirit and scope of the appended claims.

Having described my invention, what I claim is new and desire to secure by Letters Patent is:

1. The method of eliminating offset which comprises spraying on a freshly printed sheet an offset elminiating powder which consists essentially of powdered hydro genated castor oil, substantially all of said hydrogenated castor oil being of a particle size no greater than mesh.

2. The method of eliminating offset which comprises spraying on a freshly printed sheet an offset eliminating powder which consists essentially of powdered hydrogenated castor oil, substantially all of said hydrogenated castor oil being of a particle size no greater than 100 mesh, and a minor portion of a phosphate flow-promoting agent, the portion of the flow-promoting agent being sufficient that the hydrogenated castor oil flows freely.

References Cited by the Examiner UNITED STATES PATENTS 2,093,995 9/1937 Blow. 2,647,892 8/1953 La Brie et al. 101-416.2 X 2,777,776 1/ 1957 Kieras 106272 FOREIGN PATENTS 834,700 5/1960 Great Britain.

OTHER REFERENCES Warth, A. H.: The Chemistry and Technology of Waxes, 2nd, 1956. Reinhold Pub. Co., N.Y., TP670. W25, 1956, pages 471-473.

DAVID KLEIN, Primary Examiner.

J. REBOLD, ROBERT E. PULFREY, WILLIAM B.

PENN, Examiners. 

1. THE METHOD OF ELIMINATING OFFSET WHICH COMPRISES SPRAYING ON A FRESHLY PRINTED SHEET AN OFFSSET ELIMINATING POWDER WHICH CONSISTS ESSENTIALLY OF POWDERED HYDROGENATED CASTOR OIL, SUBSTANTIALLY ALL OF SAID HYDROGENATED CASTOR OIL BEING OF A PARTICLE SIZE NO GREATER THAN 100 MESH. 